IV PREFACE. 



The materials of this work have been gradually accumulating since 

 1802. They have been drawn from Scientific Journals, from the 

 Transactions of Learned Societies, and from the principal writers who 

 have flourished since the middle of the last century the Augustan 

 age of Chemistry. From works of an earlier date, light has been oc- 

 casionally derived, as well as from notes and recollections of the in- 

 structions of the distinguished teachers, to whom the author was 

 formerly so happy as to listen. In this view, he takes particular 

 satisfaction in naming the late Dr. Murray, of Edinburgh, and Prof. 

 Thomas C. Hope, still a distinguished ornament of the University in 

 the same city. 



Various notices, derived from the author's own experience, and 

 from his personal communications with others, are introduced, with 

 occasional figures, for illustration ; and in the notes, many miscella- 

 neous facts are preserved. 



In the immediate preparation of this work for the press, the origi- 

 nal memoirs of authors and discoverers have been often consulted, 

 and the abstract has been frequently drawn from them, rather than from 

 the elementary books ; but the analyses contained in the latter have 

 not unfrequently been adopted ; sometimes even after a careful ex- 

 amination of the original, and for this reason, among others, that the 

 statements contained in them could be often, without injury, still 

 farther abridged. In such cases, several eminent elementary writers 

 have been diligently compared, on the same subject ; and thus 

 omissions have been supplied, and obscurity has been removed, either 

 by the comparison, or by resorting to the first record. 



References to the original memoirs have always been preserved, 

 where such memoirs were attainable ; and when the books contain- 

 ing them were not at hand, the citations have been copied from the 

 latest systematical writers. Credit has also, in most instances, been 

 given to elementary writers, for materials drawn from their pages ; 

 but for brevity, and especially where the facts are the common 

 stock of the science, the references have been sometimes omitted, 

 or an initial letter only retained. There are, however, some works 

 to which a more particular acknowledgment is due. Those of 

 Bergman and Scheele ; the Lectures of Dr. Black, by Robison ; 

 the System of Dr. Thomson, in all its editions, and also his more 

 recent work on the First Principles of Chemistry ; the Dictionaries 



